It is completely unacceptable for a normal FS. Something a bit more advanced like ZFS may be able to cope. What I am wondering about is why amazon didn't implement such a solution on a massive scale themselves and then run EBS on top of it.
Because some users don't need reliability beyond what a normal hard drive offers, and they really shouldn't be compelled to pay for it. If you need reliability on these devices you can run software RAID or ZFS over the raw block devices being offered and tune the cost/reliability equation in whatever manner makes the most sense for your application.
